1. Field of the Invention
The present invention relates to a radiographic imaging apparatus, an imaging unit and a radiographic imaging system.
2. Description of the Related Art
The recent progress of digital technologies is popularizing a radiographic imaging apparatus which converts a radiographic image into an electrical signal, processes the electrical signal, and reproduces it on, e.g., a CRT as a visible image, thereby obtaining a high-quality radiographic image.
FIG. 7 is a conceptual view of a radiographic imaging system using the above-described radiographic imaging apparatus. A radiographic imaging apparatus 1 arranged in front of an object P incorporates a radiation detection sensor 2. A radiation generator 3 arranged behind the object P generates radiation and irradiates the object P with it. The radiation transmitted through the object P changes to visible light through the phosphor of the radiation detection sensor 2. Photoelectric conversion elements arrayed in a two-dimensional matrix detect the light as an electrical image signal. A controller 4 to control electrical signal readout from the radiation detection sensor 2 and image transfer to a monitor 5 is connected to the radiographic imaging apparatus 1. The controller 4 digitally processes the image signal read out from the radiation detection sensor 2 and displays the radiographic image of the object P on the monitor 5.
This imaging system includes a detection panel set on a frame dedicated to a specific imaging form such as a standing position or lying position and is selectively used as needed. The system is generally stationary installed in a radiographic examination room.
A recently developed portable X-ray detection unit is used when imaging in an arbitrary posture is necessary. Japanese Patent Laid-Open No. 2005-470 proposes an X-ray imaging apparatus using a portable X-ray detection unit. The X-ray imaging apparatus can stationary be supported at a position opposing the X-ray tube or separated from the support unit.
The former case allows easy positioning and quick accurate alignment. The latter case allows to place the X-ray detection unit at an arbitrary position. It is therefore possible to reduce the burden on an immovable object and take an image while adjusting the X-ray imaging apparatus to the position of the object. That is, the single X-ray imaging apparatus can cope with two imaging forms, and the convenience improves.
FIG. 8 is a view showing the arrangement of a general mobile C-arm radiographic imaging apparatus 11. A C-shaped arm member 14 is attached to the distal end of a horizontal shaft 13 supported on a main body unit 12. The arm member 14 can rotate and move as indicated by arrows. The arm member 14 has, at two ends, an X-ray generation unit 15 and an X-ray detection unit 17 opposing it and detachably attached to a holder unit 16. The arm member 14 is positioned in an arbitrary posture and used.
The X-ray detection unit 17 can take an arbitrary posture determined by rotation Rh about a horizontal shaft and rotation Rs along the track of the arm member 14 itself. Hence, the X-ray detection unit 17 takes an arbitrary posture when being detached from the holder unit 16. It is necessary to execute the operation after the posture of the arm member 14 returns to a position to easily detach the X-ray detection unit 17.
However, the above-described mobile C-arm radiographic imaging apparatus 11 may erroneously drop the X-ray detection unit 17 if its detachment direction matches the direction of gravity.